Documentation for Iterator::step_by missing `where Self: ?Sized` bound

[Manishearth]

https://doc.rust-lang.org/nightly/std/iter/trait.Iterator.html#method.step_by

https://doc.rust-lang.org/nightly/src/core/iter/traits/iterator.rs.html#391-396

The function has the following signature: fn step_by(self, step: usize) -> StepBy<Self> where Self: Sized, however the where bound does not show up in the stdlib docs.

I'm not sure what's going on here; I attempted to replicate the situation but a similarly defined trait method in a bare crate works just fine.

cc @GuillaumeGomez

[ollie27]

Duplicate of #24183